The Steed is healed! Thanks to the lovely chaps down at Two Wheels Good bike shop in Crouch End, I have my own two wheels back. I'd managed to get a wodge of fabric (the technical term) caught in my derailer, and through stubbornly trying to keep pedalling, managed to snap that off, bend the thing that holds the gear cogs (I'm sure I'll learn the proper word for that too) and also buckle the back wheel. So not a small amount of damage. I'd been bracing myself for a hefty bill, but the man with the handlebar moustache charged me to modest sum of £35. Less than a normal service.
Hurrah for having a good local bike shop- I've been ripped off and ignored by Evans too many times.
And hurrah for being back on the road- I'd missed the sensation of the wind in my hair. Steed and me restrained the urge to ring our bell with glee, because pedestrians think you're yelling at them (and sometimes I am, the dozy fools). So I just had to sing a bit whilst free wheeling down Crouch Hill instead.